Immune-mediated diseases are an emerging field of pharmacological treatment that includes autoimmune diseases, which affect approximately 5% of the population (O'Shea et al., 2002), graft rejection, allergy, atherosclerosis, infectious diseases and tumoral processes that are one major cause of mortality in industrialized countries. Therefore, the regulation of the immune response is key for the treatment of the major causes of morbidity and mortality in our society.
CD69 is expressed early and transiently following leukocyte activation after an immune challenge (Cebrian et al., 1988; Hara et al., 1986; Testi et al., 1994) in all hematopoietic subsets except erythrocytes. Although, CD69 is detected in vivo on small subsets of T and B cells in peripheral lymphoid tissues (Sanchez-Mateos et al., 1989), CD69 is persistently expressed in leukocyte infiltrates of several chronic inflammatory diseases such as rheumatoid arthritis, and viral-chronic hepatitis (García-Monzón et al., 1990; Laffon et al., 1991), in leukocytes responsible for graft rejection (Mampaso et al., 1993), in leukocytes involved in the allergic response (Hartnell et al., 1993), in immune cells at the atherosclerotic lesion (Caspar-Bauguil et al., 1998), in tumor infiltrating lymphocytes (Coventry et al., 1996), or upon persistent infection (Zajac et al., 1998). Several reports suggest that CD69 is involved in activation of bone marrow-derived cells (Cebrian et al., 1988; Testi et al., 1994). Nevertheless, nearly normal hematopoietic cell development and T cell maturation occur in CD69−/− mice under physiological conditions (Lauzurica et al., 2000).
CD69, together with two other proteins, activation-induced C-type lectin (AICL) and Lectin-like transcript (LLT1), form part of the NK complex. (Hamann et al., 1997; Boles et al., 1999). Expression of all three of these proteins, CD69, AICL and LLT1, is upregulated at early time points of cellular activation. (Eichler et al., 2001).
Autoimmune diseases are characterized by the presence of abnormal and persistent leukocyte activation that contributes to disease pathogenesis. It is well established that cytokines have essential roles in the pathogenesis of autoimmune diseases (Falcone and Sarvetnick, 1999). Therefore, the targeting of these cytokines is currently the preferred strategy in the new treatments for autoimmune disease. In this regard, tumor necrosis factor (TNF) appears to be at the top of the pro-inflammatory cascade, and anti-TNF therapy has been revealed as a useful tool for the treatment of RA (Feldmann, 2002). In addition, other cytokines have demonstrated an opposite anti-inflammatory effect. Thus, administration of TGF-β1 has beneficial effects in several autoimmune diseases (Prud'homme and Piccirillo, 2000), depressing pro-inflammatory cytokine production in arthritis (Kuruvilla et al., 1991), allergic encephalomyelitis (Chen et al., 1994), colitis (Powrie et al., 1996), and autoimmune diabetes (Piccirillo et al., 1998).
The immune response against tumors behaves as “an effective extrinsic tumor-suppressor system” that involves the combined action of humoral and cellular mechanisms, in which lymphocytes and cytokines prevent primary tumor development (Dighe A S, 1994; Kaplan D H, 1998; Shankaran V, 2001; Smyth and Godfrey, 2000; Smyth et al., 2000; van den Broek M E, 1996). Cytokine action, at least in part directed at regulating tumor cell immunogenicity, is critical for the tumor suppressor function of the immune system. Advanced tumors and metastases down-regulate class I MHC expression, becoming susceptible to NK cell killing, and therefore, NK cells recognize and destroy cancer cells. In addition, NK cells secrete cytokines, such as TGF-β and IFN-γ that drive differentiation of activated CD4 T cells into Th1 helper effector cells. In this regard, IFNγ helps to prevent tumor formation, as increased spontaneous neoplasic diseases are developed in IFNRγR−/− mice (Dighe A S, 1994; Kaplan D H, 1998). In addition, TGF-β has an important immuno-suppressive role, thus inhibiting anti-tumor immune response. TGF-β prevents and/or suppresses immune responses, regulating production of proinflammatory cytokines, reviewed in (Letterio and Roberts, 1998) and the inhibitory effect of TGF-β in the cytokine network is dependent on both cell stage and cytokine milieu. TGF-β has been implicated in the modulation of anti-tumor effector mechanisms by altering activation, proliferation and cytotoxicity of immune cells, macrophages, NK and T cells (Gorelik and Flavell, 2000; Kehrl et al., 1986). Recently, it has been reported that blockade of TGF-β signaling in T cells enhances anti-tumor immunity by facilitating an expansion of tumor specific CD8+ T cells (Gorelik and Flavell, 2001). In addition, other cytokines are important regulators of recruitment, proliferation, differentiation and survival of anti-tumor effector cells. MCP-1 produced by many cells activates cell recruitment, and animals that lack MCP-1 show diminished T cell responses (Allavena et al., 1994; Carr et al., 1994; Gu et al., 1997). Therefore, cytokines have essential roles in inducing anti-tumor immunity, and targeting cytokines provides effective therapy in human and several murine models (Gill P S, 1995).
However, the fibrogenic and other detrimental effects of TGF-β1 may limit its immunotherapeutic use in humans (Border and Ruoslahti, 1992). TGF-β has been implicated in several pathologic conditions and its systemic use has oncogenic potential, which may explain the increased number of tumors seen in patients treated with cyclosporin, a drug which enhances systemic TGF-β production (Hojo et al., 1999). Therefore, the local regulation of TGF-β1 should result in an effective treatment of chronic inflammatory diseases by avoiding the detrimental consequences of systemic TGF-β1.
Hence, CD69, AICL, and LLT1 may represent targets for immunotherapy in diseases whereby leukocytes express high levels of these activation markers. It follows that it would be desirable to develop specific antibodies to target such molecules for use in human therapy, e.g., in treating diseases associated with the presence of activated cells expressing one or more of these antigens.
Although murine monoclonal antibodies (mAbs) are relatively easy to produce, and some mouse mAbs to anti-human CD69 are now available, there are many restrictions for their therapeutic use in humans, due to their immunogenicity and to the resulting reduction in their efficacy and safety (Jakobovits, 1995). These restrictions could be overcome by the use of fully human mAbs, which would allow their repeated administration without immunogenic and/or allergic responses. Thus, the development of transgenic mice strains, engineered with unrearranged human immunoglobulin (Ig) genes, has become a good strategy for the generation of specific human mAbs.